On August 5, 1997 Congress passed the most significant funding increase for children's health care coverage since the original enactment of Medicaid, the State Children's Health Insurance Program (CHIP). As states decide how to use CHIP funds, there is an urgent need for new data about unmet health need, access to care, and crowd out among the population of children who are targeted under the legislation. Massachusetts is one of the few states in the nation that has had extensive prior experience providing health services to the population of children that are covered under CHIP expansions. The state's Children's Medical Security Plan (CMSP), initiated in July, 1994, has provided health insurance coverage for primary health care services to over 80,000 children from birth to age 18, 40 percent of whom live in families with incomes 133 percent-200 percent of the federal poverty level (FPL), the income group targeted under the CHIP expansions. Using data from CMSP administrative and claims files and information obtained from a telephone survey of CMSP participants, the proposed research aims to: 1) to determine the relationship between insurance status, unmet health need, and health service utilization among CMSP enrollees; 2) to assess the impact of enrollment in CMSP on indicators of access to health care; and 3) to determine the extent to which crowd out is occurring among CMSP enrollees. Survey findings and the linkage of survey data with claims data are expected to assist in estimating health needs and costs of children likely to enroll in CHIP programs. Survey questions related to unmet health need and access to care are modeled after those from the NHIS Access to Care Module. Questions related to family demographics and insurance status based on the 1998 random household survey of Massachusetts' residents insurance status to enable comparison to the state's population. The study population is currently enrolled children who have been continuously enrolled for a minimum of 6 months. A sample of 900 program participants stratified by income group (less than 133, 133-200, greater than 200 percent FPL) and age and systematically selected by date of enrollment will yield estimates with sampling errors of +/-3 percent at a 95 percent CI for major research questions. Interviews will be conducted in Spanish and Portuguese among respondents more comfortable in their native language. An additional over sample of 100 Spanish speaking respondents is proposed to permit stable inferences specific to the Spanish speaking enrollees. Using the McNemar test to assess within subject changes related to unmet health need and access indicators pre and post program enrollment, the study design has greater than 85 percent power to detect changes. Multiple and multinomial logistic regression models will be used predict relationships between major outcomes (crowd out and health service utilization) and primary question variables (length of time without insurance, access indicators, unmet health need, and family demographics).